Field of the Invention
The present invention relates to a projection type color liquid crystal optical apparatus comprising a light source system for projecting light, color separating and synthesizing dichroic mirrors, three reflection type liquid crystal optical elements and a projection lens as its constituent elements.
In recent years, a transparent/scattering type liquid crystal optical element in which a liquid crystal and solidified matrix composite is held wherein a nematic liquid crystal is dispersed and and held in a solidified matrix, and the refractive index of the solidified matrix is made substantially coincident with the refractive index of the liquid crystal used in either state of application or non-application of a voltage, has been noted. The transparent/scattering type liquid crystal optical element has an advantage enabling a bright display because no polarization plate is used. Therefore, the optical element is gathering an attention when it is, in particular, used for a projection type optical apparatus because a bright projection picture image is obtainable.
When the transparent/scattering type liquid crystal optical element is used as a reflection type element wherein a light reflection layer is formed on a surface of the element, light is reciprocated in a layer of a light modulating material so that there is obtainable a working length twice as large as a case of using the optical element as a transmission type element, whereby it can be used as an element having a high scattering ability in a scattering stage.
Accordingly, when the transparent/scattering type liquid crystal optical element is used for the reflection type optical apparatus, there is a clear difference between a transparent state and a scattering state, and a high contrast display becomes possible in comparison with a case of the transmission type optical apparatus.
Further, a projection type color liquid crystal optical apparatus wherein the transparent/scattering type liquid crystal optical element is used as a reflection type element, in particular, a projection type color liquid crystal optical apparatus wherein light from a white light source is subjected to color-separation into three colors: blue (B), green (G) and red (R), and each of the color lights is modulated with use of three reflection type liquid crystal optical elements, is useful because full color projection becomes possible by regulating light scattering properties of the reflection type liquid crystal optical elements.
Further, it has been proposed a full color projection type display apparatus using a reflection type liquid crystal display element wherein an electrode in a back electrode substrate is constituted by divided picture element electrodes, and each of the picture element electrodes is driven by an active element such as a TFT or the like which is provided for each picture element.
When the active element and a storage capacitor are formed for each of the picture elements, reduction in a numerical aperture ratio of a picture element due to the formation of the capacitor in the reflection type liquid crystal display element can be eliminated whereby a high aperture ratio can be obtained in comparison with that of a transmission type liquid crystal display element. Further, flexibility in designing the active element such as TFT can be increased.
As a projection type color liquid crystal optical apparatus in which the transparent/scattering type liquid crystal optical element is used as a reflection type element, there is described a projection type liquid crystal display apparatus in, for instance, Japanese Unexamined Patent Publication No. 502286/1986 wherein a single reflection type display element having color filters of blue, green and red in a mosaic form is used. However, the publication does not describe a color projection system wherein light from a white light source is subjected to color separation into three colors of B, G and R, and each of the color lights is modulated with use of three reflection type elements.
Regarding to the projection type color liquid crystal display apparatus wherein the transparent/scattering type liquid crystal optical element is used as a reflection type element, light from a white light source is subjected to color separation into three color lights of B, G and R, and the color lights are modulated with use of three reflection type elements, the construction of an optical system used in the display apparatus is described in FIG. 5 of Japanese Unexamined Patent Publication No. 142528/1992, or FIG. 1 of Japanese Unexamined Patent Publication No. 232917/1992.
In each of the publications, an ellipsoidal mirror is used for a condenser mirror in a light source optical system. Light emitted from the light source optical system is rendered to be parallel light beams with use of a single convex lens, and the parallel light beams are incident into each reflection type element of the three transparent/scattering type liquid crystal optical elements.
Dichroic prisms intersecting at an angle of 45.degree. are arranged as a color separating and synthesizing system between the convex lens for parallel light beams and the reflection type elements. The conventional technique is shown in FIGS. 18 and 19. FIG. 18 is a plane view of the optical system wherein the light source optical system and a projection lens are omitted, and FIG. 19 is a side view showing the entirety of the optical system. As a result, it is necessary to provide spaces between a projection lens 142 and a convex lens 130 for forming parallel light beams and between a light source optical system 101 and the convex lens 130 for parallel light beams to thereby result an increase in volume of the color projection type liquid crystal display apparatus.
Further, dichroic prisms 102 can allow optical adjustment to be easy and to advantageously shorten the optical path in comparison with flat plate type dichroic mirrors generally used in the conventional projection type color liquid crystal display apparatus using transmission type liquid crystal optical elements. However, use of the dichroic prisms 102 increases the weight and results in a higher manufacturing cost.
Further, incident light to and reflection light from reflection type liquid crystal optical elements 131, 132, 133 are not on the same optical axis but they are entered and reflected with certain angles with respect to the reflection surface of the reflection type liquid crystal optical elements. Accordingly, in order to utilize light without loss, the effective surfaces of a color separating and synthesizing system 102 and the convex lens 130 for parallel light beams should have a larger surface area in comparison with the reflection surface of the reflection type liquid crystal optical elements; this causing an increase in the volume and weight of the apparatus.
Further, the convex lens 130 for parallel light beams influences the imaging function of the projection lens 142 with respect to the three color lights of B, G and R. Accordingly, when the convex lens is used for a projection type display apparatus, it is necessary to combine two or more number of lenses to reduce chromatic aberration, this resulting in a complicated structure.
On the other hand, in place of the dichroic prisms intersecting at an angle of 45.degree. which are used for a color separating and synthesizing system, a construction shown in FIGS. 20 and 21 wherein flat plate type dichroic mirrors are crossed at an angle of 45.degree., can be considered.
FIG. 20 is a plane view and FIG. 21 is a side view wherein reflection type liquid crystal optical elements 231, 232 for lights reflected and separated by the dichroic mirror 202 are omitted. In this case, although lightweighting effect and a cost reduction can be achieved in comparison with a case of using the dichroic prism, there is a problem that the shadow of the crossing part of the dichroic mirrors is apt to be projected on a screen. This causes a serious problem of deteriorating the quality of display by the projection type display apparatus.
Further, in a projection type color display apparatus using a conventional transmissive type liquid crystal optical element, since two kinds of dichroic mirrors are generally used for a color separating system and a color synthesizing system respectively, there is flexibility in adjusting the color purity of the three colors of B, G and R by using four dichroic mirrors.
However, in a case of a projection type color liquid crystal display apparatus using a reflection type liquid crystal optical element, it is necessary to adjust the color purity of the three colors of B, G and R by using two kinds of two dichroic mirrors as shown in FIGS. 18 through 21. Under such condition, when a white light source having a high color rendering property and a high luminous efficacy such as a metal halide lamp, a xenon lamp, a halogen lamp or the like is used as a projection light source, excellent color purity in three colors of B, G and R can not be attained.
A reflection type display element using a visco-elastic material as a light modulating material is disclosed, for instance, SPIE VOL. 1255, "Large-Screen Projection Display (1990), page 69-78".
In the reflection type display element, a voltage is applied to the visco-elastic material by means of an active element which is provided for each picture element electrode whereby the reflection surface of the viscoelastic material is deformed depending on an applied voltage to thereby form a diffraction grating. When incident light is irradiated thereto, a diffraction light is produced.
In order to display a projection image having a high contrast ratio, a dark field schlieren optical system in which a schlieren stop is or schlieren bars are used to block a non-diffraction light. This provides a transparent state (a non-diffraction state) when no voltage is applied unlike a case that the liquid crystal and solidified matrix composite is used for a transparent/scattering type display element. Accordingly, the dark field schlieren optical system is used in order to make a non-voltage application state to be in a dark level display.
FIGS. 22 through 24 show three kinds of optical systems explained in the above-mentioned publications.
FIG. 22 shows an optical system in which a schlieren stop is used as a non-diffraction light rejecting system; FIG. 23 shows an optical system in which a schlieren bars are used as a non-diffraction light rejecting system; and FIG. 24 shows an optical system in which a schlieren stop is used as a non-diffraction light rejecting system, and condenser lenses are used at a light source side and a projection side to transform incident light with respect to color separating and synthesizing dichroic mirrors into parallel light beams.
FIG. 22 to 24 shows light source LS, (light source) lens LC, dichroic mirror 21 and 22, lens L1, L2, L3, and optical display element E1, E2, E3, light converging lens L4 and so on.
In these optical systems, the visco-elastic material is not deformed when no voltage is applied, and a zero-order diffraction light (non-diffraction light) is blocked by the schlieren stop or the schlieren bars whereby light is not projected on the screen. Accordingly, while a dark level in a picture image can be controlled to have a lower value, a bright level does not form a bright projection image unless diffraction intensity is sufficient.
Further since the projection light is a component of a diffraction light, collimation is uneven. When the length of a light path reaching the projection lens is large, light is scattered and lost in an intermediate portion of the light path, and light flux projected on the screen is reduced. Further, a projection lens having a large aperture is necessary in order to efficiently collect the diffraction light on the screen.
Accordingly, in the dark field schlieren optical system used for a reflection type display element using a visco-elastic material, since a diffraction light in which collimation is lost is used as a projection light, the light is scattered and lost in a way to reach the projection lens, or light is rejected at the aperture of the projection lens when the ordinary optical system is used, and an amount of the light reaching the screen is disadvantageously reduced. In order to reduce a light loss as described above, a large-sized color separating and synthesizing system (dichroic mirrors) and a projection lens having a large aperture are needed; this inviting a large-sized apparatus.
In the above-mentioned publications, advantages and disadvantages are described on the three kinds of optical systems shown in FIGS. 22 through 24. However, the optical systems involves the above-mentioned problems, and conclusion is not provided as to which form is finally preferred. Accordingly, in a projection type color liquid crystal optical apparatus in which a transparent/scattering type liquid crystal optical element is used for a reflection type liquid crystal optical element, an apparatus of a small size, a light weight and having a high color purity is expected.
Further, J. E. Gunther, in "High Visibility Color Projection Display" (final technical report), HAC reference number F2317, (1986) discloses a projection type display apparatus in which three reflection type liquid crystal display elements comprising active elements formed of singlecrystalline silicon and a DSM type liquid crystal as a light modulating means are used, and a prism block of three prisms is used as a color separating and synthesizing optical system (refer to FIG. 31).
In the disclosed projection type display apparatus, the incident angle of light to a dichroic mirror surface is 45.degree. or lower, and sharpness in color separation and synthesization is high in comparison with a dichroic mirror or a dichroic prism having a 45.degree. light incidence structure. Accordingly, the color purity of a projection light is high. However, the projection type display apparatus had disadvantages that three prisms are required for a prism block, and the length of a light path between a condenser lens 830 and a display elements 831, 832, 833 is long in comparison with a 45.degree. incidence-intersection type color separating and synthesizing system shown in FIGS. 18 through 21.
Generally, a white color light source such as a metal halide lamp, a xenone lamp, a halogen lamp or the like which has a high brightness of luminescence and a long life of luminescence does not provide a complete point source. Accordingly, it is difficult to focus light to a point even when light is collected by means of a lens in the light source system shown in the Figures. Further, parallel light beams having good collimation can not be obtained even when a lens 830 is used to make light reflected from a reflection plate to be parallel light beams. Thus, when an incident light to a liquid crystal display elements is not complete parallel light beams, a part of the light is not incident to the liquid crystal display elements but escapes from a side surfaces of a prism block, and a part of the light without collimation which is produced by the total reflection at the side surface of the prism is entered into the liquid crystal display elements.
Further, there is a possibility that a part of specular reflection light to be projected, which has been reflected at the reflection surface of the liquid crystal display elements and has passed through the prism to be projected finally, escapes from the side surface of the prism block, or a part of the specular reflection light is totally reflected at the side surfaces of the prism block, whereby the light does not enter into a projection lens.
The above-mentioned incident light of non-collimation does not contribute to the brightness of projection light since specular reflection of light is caused by the liquid crystal display elements in a transparent state and the light of specular reflection is not incident into the projection lens. Instead, the light is incident into the projection lens when the liquid crystal display element is in a scattering state. Accordingly, a dark level is increased. As a result, the brightness of the projection light is decreased and the contrast ratio of a display is deteriorated.
This requires to use a sufficiently large prism in comparison with a display area of the liquid crystal display element in order to realize a predetermined characteristic even when a practical light source is used. Accordingly, the weight of the apparatus is substantially increased. Further, with respect to light incident to the liquid crystal display element 831, it is necessary to form the incident light entering to a prism block to be parallel light beams because the light is totally reflected at the surface of a prism after it is color-separated in a dichroic mirror 821. Further, the focal length of an imaging lens is generally longer than the lens diameter. As a result, a large-sized projection lens system including a lens 830 for forming parallel light beams is required, so that the volume of the apparatus is increased.
Further, the incident angle of incident light to a liquid crystal display element is different from the incident angle of reflection light reflected at the liquid crystal display element with respect to the surface of the dichroic mirror 821 or 822 shown in FIG. 31. Accordingly, the spectral characteristics of the dichroic mirror at positions in the same dichroic mirror surface are varied whereby there causes the reduction of light utilization efficiency and stray light.
Japanese Unexamined Patent Publication No. 113344/1992 discloses a projection type display apparatus wherein a projection light source system comprises a light source, an ellipsoidal mirror, an aperture and a condenser lens. Specifically, the ellipsoidal mirror is used as a condenser mirror; the light source is disposed at the first focal point of the ellipsoidal mirror, light from the light source is collected to the second focal point position; light passing through the opening of the aperture disposed at the second focal point position is collected by the condenser lens; the collected light is introduced into a transparent/scattering type display element; light emitted through the display element is collected to a focal point position; and a second aperture having an opening is disposed at the focal point position. In the above-mentioned publication, there is reference to the use of a reflection type liquid crystal display element.
Further, Japanese Unexamined Patent Publication No. 142528/1992 and Japanese Unexamined Patent Publication No. 305637/1992, describe examples concerning a reflection type display apparatus in combination of the above-mentioned projection type display apparatus, a color separating and synthesizing system and three transparent/scattering display elements.
The present invention is to solve the above-mentioned problems and to provide a projection type color liquid crystal optical apparatus of a small size, a light weight and having a high color purity.
As the basic construction of the present invention, there are a three reflection type liquid crystal optical elements arranged in a .DELTA. (delta) form at an angle of about 60.degree. in a horizontal plane (a specific plane); a color separating and synthesizing optical system comprising two type dichroic mirrors arranged in a V form at an included angle .beta. of about 60.degree. and an optical arrangement for look-up (look-down) projection wherein light is emitted obliquely upwardly (or downwardly) from a light source optical system in a direction of a vertical plane with respect to the above-mentioned horizontal plane in a course from the light source system through the liquid crystal optical elements to a projection optical system; the emission light is incident into the color separating and synthesizing system, and the light is reflected at a reflection type liquid crystal optical element to be directed upwardly (downwardly). Wherein there is relationship of .beta.=.alpha.1+.alpha.2. FIG. 27(a) shows perspective view of one embodiment of projection type color liquid crystal optical apparatus and FIG. 27(b) show the light path (optical axis AX) going to/coming back from the reflection layer. There is a case that the dichroic mirrors 21, 22 are a little bit inclined normal plane for H.sub.p.
Namely, in accordance with the present invention, there is provided a first projection type color liquid crystal optical apparatus, comprising light source system, light modulating system, wherein three liquid crystal optical elements having a transparent/scattering type operation mode and liquid crystal and solidified matrix composite layer where a nematic liquid crystal is dispersed and held in a solidified matrix, is interposed between a front substrate with a transparent front electrode and a back substrate with back electrode, and the refractive index of the solidified matrix substantially agrees with the refractive index of the nematic liquid crystal used in either state of the application or the non-application of applied voltage for said liquid crystal and solidified matrix composite layer; three reflection layers; and three condenser lenses are arranged; color separating and synthesizing optical system wherein two color separating and synthesizing means are arranged substantially at an angle .beta. in the range of 40.degree.-70.degree. in a horizontal plane; and light projection optical system; wherein the optical axis from light source system to light projection optical system is arranged in a look-up or down projection form in the substantially normal plane with respect to said horizontal plane; and the light emitted obliquely and upwardly or downwardly from light source travels through said color separating and synthesizing optical system and said light modulating system along the optical axis wherein the first color separating and synthesizing means is set to have an incident angle .alpha.1 for optical axis in the range of about 20.degree.-35.degree., the second color separating and synthesizing means is set to have an incident angle .alpha.2 for optical axis in the range of about 20.degree.-35.degree., and the light is separated into the three color lights and modulated respectively by said each liquid crystal optical element and reflected respectively with an incident angle .gamma. in the range of 1.degree.-20.degree. by said each reflection layer and converged respectively by said each condenser lens; and the modulated and converged three color lights are synthesized and enters into said light projection optical system to be projected.
In the first projection type color liquid crystal optical apparatus, it is not always necessary that .alpha.1 and .alpha.2 are completely in coindence with each other.
Further, the definition of the angle in a horizontal plane means an angle obtained when two dichroic mirrors (flat type) are projected on a certain flat plane, or an angle cross-sectioned along the flat plane. For instance, the angle .beta. appears on the plane in FIG. 1.
In accordance with the present invention, there is provided a second projection type color liquid crystal optical apparatus, wherein in the first projection type color liquid crystal optical apparatus, wherein the angle .alpha.1 is nearly equal to the angle .alpha.2 and the angle .gamma. is in the range of about 2.degree.-10.degree..
In the second projection type color liquid crystal optical apparatus, it is preferable that the angle .alpha.1 is set to be about 30.degree.(.beta.=60.degree.).
In accordance with the present invention, there is provided a third projection type color liquid crystal optical apparatus, wherein in the first or the second projection type color liquid crystal optical apparatus, wherein the three condenser lenses are attached on the front side of the each liquid crystal optical element respectively.
In accordance with the present invention, there is provided a fourth projection type color liquid crystal optical apparatus, wherein in any of the first through the three projection type color liquid crystal optical apparatus, wherein the three reflection layers are fabricated in the three liquid crystal optical elements respectively.
In accordance with the present invention, there is provided a fifth projection type color liquid crystal optical apparatus, wherein in any of the first through the fourth projection type color liquid crystal optical apparatus, wherein the condenser lenses are arranged between the liquid crystal optical element and the color separating and synthesizing means respectively and an charge transfer plate (CTP) is used for the back substrate of the liquid crystal optical element where a CTP in which a number of thin electric conductive wires are embedded in an insulating material is provided; said reflection layer is interposed between said CTP and the layer of the liquid crystal and solidified matrix composite.
In accordance with the present invention, there is provided a sixth projection type color liquid crystal optical apparatus, wherein in any of the first through the fifth projection type color liquid crystal optical apparatus, wherein the light source system comprises a ellipsoidal reflection mirror, a light source and a aperture wherein the light emitting part of the light source is located in the vicinity of the first focal point of the ellipsoidal reflection mirror and the opening of the aperture is located in the vicinity of the second focal point of the ellipsoidal reflection mirror and a cone-like prism or a cone-like reflector is arranged in the vicinity of the second focal point of the ellipsoidal mirror.
So preferable collimation angle of the light from light source such as 6.degree.-10.degree. is obtainable.
In accordance with the present invention, there is provided a seventh projection type color liquid crystal optical apparatus, wherein in any of the first through the sixth projection type color liquid crystal optical apparatus, wherein said liquid crystal optical element comprising a transparent insulating front substrate and a back substrate where a plurality of row electrode lines, column electrode lines, active elements disposed in the vicinity of each intersection of the row and column electrode lines, a multi-layered dielectric film mirror for covering partly or entirely the row electrode lines, the column electrodes lines, and active elements are provided; and the pixel electrodes are transparent electrodes formed on or above said multi-layered dielectric film mirror.
In this characteristic structure of transparent electrode on/above mirror in TFT substrate is available for single liquid crystal optical device.
In accordance with the present invention, there is provided a eighth projection type color liquid crystal optical apparatus, wherein in any of the first through the seventh projection type color liquid crystal optical apparatus, wherein said liquid crystal optical element comprising a transparent insulating front substrate and a back substrate where a plurality of row electrode lines, column electrode lines, active elements disposed in the vicinity of each intersection of the row and column electrode lines and the third electrode are provided; and said third electrode is arranged so as to cover partly or entirely the row electrode lines, the column electrode lines and the active elements and/or to cover substantially the gap between the neighbouring pixel electrodes; and the electric potential between said third electrode and said front electrode is kept to be equal to or to be lower than the threshold level of the liquid crystal and solidified matrix composite.
In this projection type color liquid crystal optical apparatus, a functional drawback caused by the neighbouring pixel gap in reflection type liquid crystal optical element is improved and good aperture ratio is obtained and lower driving voltage is available due to electrical efficiency for liquid crystal and solidified matrix composite. Also, this third electrode structure and biasing with substantially the same level of front electrode in liquid crystal optical element having liquid crystal and solidified matrix composite is available for single LCD panel application.
In accordance with the present invention, there is provided a ninth projection type color liquid crystal optical apparatus, wherein in any of the first through the eighth projection type color liquid crystal optical apparatus, wherein either the first or the second color separating and synthesizing means is provided with a distribution in a manner that the spectral transmittance changes at position in each surface so as to compensate the difference of the spectral transmittance corresponding to the difference of light incident angle at said position.
In accordance with the present invention, there is provided a tenth projection type color liquid crystal optical apparatus, wherein in any of the first through the ninth projection type color liquid crystal optical apparatus, wherein the reflection layer is provided with a multi-layered dielectric film having a relatively high refractive index and a relatively low refractive index alternately.
In accordance with the present invention, there is provided a eleventh projection type color liquid crystal optical apparatus, wherein in any of the first through the tenth projection type color liquid crystal optical apparatus, wherein minute concave and convex are formed on the surface of front electrode or the interface of the front substrate.
In accordance with the present invention, there is provided a twelfth projection type color liquid crystal optical apparatus, wherein in any of the first through the eleventh projection type color liquid crystal optical apparatus, wherein a wavelength selecting and reflecting function of the reflection layer for compensating the color purity characteristic of the first and/or second color separating and synthesizing means is provided with at least one of the three reflection layers.
In accordance with the present invention, there is provided a thirteenth projection type color liquid crystal optical apparatus, wherein in any of the first through the twelfth projection type color liquid crystal optical apparatus, wherein wavelength selecting and absorbing function for compensating the color purity characteristic of the first and/or the second color separating and synthesizing means is provided with at least one of the condenser lens, the reflection layer or the liquid crystal optical element.
Further description is followed after.
In the projection type color liquid crystal optical apparatuses of the present invention, a liquid crystal optical element used has many advantages compared with conventional DSM or TN LCD element.
For example, the structure of the liquid crystal and solidified matrix composite such as capsule size R, shape, density are possible to be suited for wavelength region of color light. For example, R.sub.B &lt;R.sub.G &lt;R.sub.R of capsule size is available.
Further, the specific resistance of the liquid crystal and solidified matrix composite is preferably 5 .times.10.sup.9 .OMEGA.m or higher. In order to minimize voltage drop due to a leak current or the like, a specific resistance of 10.sup.10 .OMEGA.cm or higher is more preferable. In this case, it is unnecessary to provide a larger storage capacitor to each picture element electrode.